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  #1 (permalink)  
Old 06-28-2018, 8:33 PM
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Default Choppy audio on P25 Phase 2

Before I submit a bug report, I'm curious if others have experienced choppy sounding audio as well on the TRX-1 when monitoring P25 Phase 2 talkgroups.

Symptom: Speaker/headphone audio drops out very briefly about 3 times per second on more than half of the P25 Phase 2 transmissions, but these dropouts are not present in the TRX-1's recordings of the transmissions.

Discussion: The dropouts happen on precise 360 millisecond intervals and last 19 milliseconds (241 ms of audio followed by 19 ms of silence). When they are present they affect the entire transmission. They never begin or cease mid-transmission. I've found no rhyme or reason as to why they affect some transmissions but not others, and have tested it on two separate p25 phase 2 systems with identical results. (Both Phase 2 systems tested were simulcast systems.) Phase 1 talkgroups on those systems are unaffected.

The dropouts are clearly visible in the Audacity waveform screen capture at this link:

https://www.dropbox.com/s/zkhuz6xgwk...ecord.jpg?dl=0

The top track in the capture was recorded using the TRX-1's internal recorder, and the lower track with dropouts was recorded by Audacity from the headphone jack.

The audio file depicted in the screen capture can be heard at the following link:

https://www.dropbox.com/s/hlozwo8ma6...ecord.mp3?dl=0

The internal recording is on the left channel and the Audacity recording from the headphone jack is on the right.

This audio file contains a longer, 50-second sample of the choppy audio as recorded from the headphone jack.

https://www.dropbox.com/s/iz4dpo61me...ample.mp3?dl=0

I read somewhere that P25 Phase 2 data streams utilize a "superframe" which is 360 milliseconds in length. This leads me to speculate that when the problem occurs, the TRX-1 squelch gate may be erroneously closing at the end of each superframe. Note that these experiments were all conducted with the squelch knob fully open (counterclockwise), and that its position had no impact on the dropouts.

I also monitored the dropouts while simultaneously tracking the P25 system on Unitrunker to see if there was any correlation with certain channels or time slots, or with other activity on the system. I found none. Even when the conversation remained on the same channel and time slot, often one transmission would be choppy and the reply would be fine, or vise versa.

Location or position of the scanner also had no impact, and there were no active priority channels. The fact that the TRX-1 audio recordings are unaffected would seemingly rule out reception problems.

I first noticed this problem in December 2016 after a firmware upgrade, but I had only used the scanner a very short time and don't know for sure whether it had been present before the upgrade. At first I assumed it to be LSM distortion, but that does not appear to be the case.

Greg
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Old 06-29-2018, 11:43 AM
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Have you tried adjusting the thresholds?
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Old 06-29-2018, 12:13 PM
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Quote:
Originally Posted by Wackyracer View Post
Have you tried adjusting the thresholds?
Yes, that was my first tactic when I assumed it was LSM distortion. I followed the recommendation in various threads and tried multiple times, but it never seemed to make any difference.
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Old 06-29-2018, 1:46 PM
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Quote:
Originally Posted by dem1 View Post
Symptom: Speaker/headphone audio drops out very briefly about 3 times per second on more than half of the P25 Phase 2 transmissions, but these dropouts are not present in the TRX-1's recordings of the transmissions.
The transmission must then be received without any problems and it is the audio to the speaker/headphone audio that has some kind of firmware bug. It most probably are a bug in the muting function from the digital decode routine that controls the mute of the final audio power amplifier.

scannerbugreports@whistlergroup.com

/Ubbe
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Old 07-10-2018, 12:47 PM
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I'm having the same problem. Any solution?
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Old 07-12-2018, 1:51 PM
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Quote:
Originally Posted by Bobzee View Post
I'm having the same problem. Any solution?
Yes. Buying the next generation scanners from Whistler and Uniden that supposedly fix this problem the right way. The TRX-1 and TRX-2 just cannot handle phase II systems with linear simulcasting in play. The new Uniden SDS100 supposedly has this problem solved. Whistler's new scanner is coming soon supposedly.
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Old 07-12-2018, 2:22 PM
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Quote:
Originally Posted by Skypilot007 View Post
Yes. Buying the next generation scanners from Whistler and Uniden that supposedly fix this problem the right way. The TRX-1 and TRX-2 just cannot handle phase II systems with linear simulcasting in play. The new Uniden SDS100 supposedly has this problem solved. Whistler's new scanner is coming soon supposedly.
New models are slated for end of the year for whistler.

Rumor is a firmware upgrade for audio issues is in the works.
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Old 07-12-2018, 8:12 PM
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Whistler contacted me in response to my bug report and a fix is forthcoming.
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Old 07-13-2018, 1:03 PM
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Quote:
Originally Posted by dem1 View Post
Whistler contacted me in response to my bug report and a fix is forthcoming.
Any fix for the TRX- and TRX-2 will be a patch job and most likely not effective. Especially in a mobile application. These scanners simply do not have the proper hardware to demodulate linear simulcasting phase II systems. I hope they can fix it as I own a TRX-2 but I'm not getting my hopes up. My TRX-2 is nearly useless on the phase II systems in my area. I've tried all the suggestions put forth here in the forums but nothing works.
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Old 07-13-2018, 1:33 PM
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Skypilot007, my original post in this thread and bug report, as well as Whistler's forthcoming fix, pertain to a specific fault unrelated to LSM distortion. As you note, that matter can only truly be resolved with new hardware.
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Old 07-13-2018, 1:42 PM
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Quote:
Originally Posted by Skypilot007 View Post
Any fix for the TRX- and TRX-2 will be a patch job and most likely not effective. Especially in a mobile application. These scanners simply do not have the proper hardware to demodulate linear simulcasting phase II systems. I hope they can fix it as I own a TRX-2 but I'm not getting my hopes up. My TRX-2 is nearly useless on the phase II systems in my area. I've tried all the suggestions put forth here in the forums but nothing works.
He has a audio issue not a LSM issue.
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Old Today, 9:02 AM
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I own a TRX-2 for home searching use, and just purchased aTRX-1 for mobile/portable searching use.

Although I have not experienced this issue, I'm waiting for a resolution. Hopefully a firmware fix is just around the corner.

Phil
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